Mechanism which includes an object arranged to travel freely on a surface

ABSTRACT

A device for use as a toy or in driver instruction in which a toy or model vehicle is guided over a marked upper surface by a motor-driven object that is freely movable over an underlying lower surface. A magnetic link is established between the object and the toy or model vehicle and the object is steered by controlling the speeds of rotation of its wheels. A flat striplike cable supplies electric power to the object and tangling of the cable is avoided by surrounding the object with a member which is rotatable relative thereto, the cable extending between said member and a fixed control panel.

United States Patent [151 3,638,357

Gl'Oh Feb. I, 1972 [54] MECHANISM WHICH INCLUDES AN PrimaryExaminerLouis G. Mancene OBJECT ARRANGED TO TRAVEL FREELY ON A SURFACElnventor: Karl Heinz Groh, 2, 8752 Mainsschaff uber Aschaffenburg,Sandvveg, Qe rman y Filed: July 2, 1969 Appl. No.: 838,399

Foreign Application Priority Data 5/1953 Pastorius ...46/2g0 AssistantExaminer-J. Q. Lever Attorney-Cushman, Darby & Cushman ABSTRACT A devicefor use as a toy or in driver instruction in which a toy or modelvehicle is guided over a marked upper surface by a motor-driven objectthat is freely movable over an underlying lower surface. A magnetic linkis established between the object and the toy or model vehicle and theobject is steered by controlling the speeds of rotation of its wheels. Aflat striplike cable supplies electric power to the object and tanglingof the cable is avoided by surrounding the object with a member which isrotatable relative thereto, the cable extending between said member anda fixed control panel.

Claims, ll Drawing Figures sls'ssgssv PATENTED FEB 1 19 2 saw 3-10; 5

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PATIENTEB rm H912 SHEET h -0F 5 FIG. IO

Invenhr M l Hem; Groiwah A, A-hbrneys MECHANISM WHICH INCLUDES AN OBJECTARRANGED TO TRAVEL FREELY ON A SURFACE This invention relates to deviceswhich comprise an object that is motor driven in such a way that it canmove freely on a surface in response to electric current which itreceives from a stationary control panel through the intermediary of aflexible cable and a multiple slip ring mounted on said object.

Such a device may be designed, for example, to cause toy or modelvehicles to travel over a further overlying surface in a realisticmanner, such toy or model vehicles thus being controlled from the panelmentioned above. For steering the object in such a device, it isnecessary to ensure that the flexible electricity supply cable whichinterconnects the object and the control panel does not become entangledwith itself and that the travelling object can perform any movement, forexample a large number of circular movements, without the supply cablegiving difficulties.

According to the invention, there is provided a device comprising anobject that is motor driven in such a way that it can move freely on asurface in response to electric current which it receives from astationary control panel through the intermediary of a flexible cableand a multiple slip ring mounted on said object, wherein the object issurrounded by a member which is rotatable relative to the object, saidmember being formed with a cylindrical outer surface around which thecable, that is of flat striplike formation, can wind, and wherein thesurrounding member includes a support for a plurality of contacts thatare connected to corresponding conductors of said cable and are also inwiping engagement with corresponding rings of the multiple slipring theconstruction and arrangement of the device being such that, during theuse thereof, the object travelling in response to electric currentreceived from the panel can cause toy or model vehicles to travel over afurther surface in a realistic manner.

The further surface will normally be located over and above the surfaceupon which the travelling object is freely movable and can be marked,and/or physically provided as appropriate, with roads, squares, trees,houses and so on so that a child or other person can sit at the controlpanel and operate a steering wheel generally similar to that of a motorcar. The supply cable is invisibly located beneath the upper surface onwhich at least one toy or model vehicle travels and, clearly, is notimpeded by any model houses, trees or other objects mounted on saidupper surface. Instructional devices can be similarly made for use inteaching driving, it being readily possible for the controls to beconstructed in the same general way as those of an average motor car sothat a pupil can see, as an outside observer, what effect his steeringhas upon the toy car which he is controlling on the upper surface ofthedevice.

The travelling object located on the lower surface may comprise, for thetransmission of its movement to the toy or model vehicle located on theupper surface, an upwardly directed permanent magnet which will belocated immediately beneath the upper surface and which will thus carrythe overlying toy or model vehicle with it provided that said toy ormodel vehicle is constructed from, or provided with, a magneticallyactive material. It will be evident that the plate which affords theupper surface should be formed from a magnetically inactive materialthrough which a magnetic field can pass without hindrance when the driveis to be transmitted from the lower moving object to the upper toy ormodel vehicle in this way.

The lower travelling object may comprise a signal generator which isadapted to be actuated through the supply cable and which acts on asignal receiver disposed in the overlying toy or model vehicle. In thisway, a number of signals can be transmitted to the toy or model vehicleas well as simple steering movements. For instance, a toy or modelvehicle such as a crane or dredger may have its moving parts operated inthis way. There may be employed as the signal generator an upwardlydirected rotary magnet which drives a corresponding downwardly directedmoving magnet or a moving iron in a receiver portion of the toy or modelvehicle. The moving magnet in the lower travelling object is controlledthrough the supply cable from the control panel, while the moving magnetor moving iron is arranged to actuate, for example, the arm of ahoisting crane in the toy or model vehicle.

Signal transmission may also be effected by means of a verticallymovable lifting magnet which raises and lowers a magnet or iron memberof like or opposite polarity disposed in the receiver portion of the toyor model vehicle. The signal generator may also be a rocking magnetwhich actuates a rocking magnet or rocking iron member in the receiverof the toy or model vehicle. The signal transmission from the signalgenerator to the signal receiver may also be effected by means of highfrequency, ultrasonically or optically.

The lower surface on which the lower traveling object moves may comprisea magnetically active layer and the lower object itself may be equippedwith means for generating a downwardly directed magnetic field. This hasthe advantage that the whole device need not necessarily be horizontallydisposed and could, in an extreme case, be located with both of thetravelling surfaces vertically disposed. The lower travelling object isthen prevented from falling off the surface on which it travels byvirtue of its magnetic adhesion thereto and the same applies to the toyor model vehicle which is magnetically linked to the surface justmentioned through the intermediary of the travelling object. In the caseof a device adapted for use in driving instruction, the pupil may beseated at a control panel simulating the controls of a motor car and canobserve the movement of a model motor car on a vertical plane disposedin front of him, said model motor car being arranged to move inaccordance with the steering imparted to it by the pupil.

The upper surface of the device upon which the or each toy or modelvehicle moves may take the form of a nonmagnetic foil stretched over awooden frame in the manner of a drum skin so as to extend parallel tothe lower surface upon which the travelling object moves withoutappreciable deformation of the shape of the wooden frame. Alternatively,both the frame and the upper surface may be formed from syntheticplastics materials.

it has been found that the multiple slipring may take the form of aslipring plate having concentric sliprings that are engaged bycorresponding sets of wiping contacts. It is advantageous for themultiple slipring to comprise a plurality of sliprings disposedcylindrically around the whole, or a part, of the lower travellingobject. In one construction in accordance with the invention, a ring maybe movable around the lower travelling object with the aid of acorresponding rotary counting and may carry a contact bridge for thesliprings, the con tact bridge being connected to the supply cable. Thesupply cable itself is of flat striplike formation and it has been founddesirable to strengthen the cable strip by including therein threads ofnonelectrically conducting material that have a high resistance tobreakage.

The lower travelling object advantageously takes the form of a carriagehaving two juxtaposed individually driven wheels. The travelling objectcan then be steered in a simple manner by adjustment of the speeds ofthe rotation of the two wheels. Each wheel may be driven by acorresponding small electric motor whose speed is related to the appiiedvoltage so that differences in the speed of rotation of the two wheelscan be effected by adjusting the voltages applied to the two motors.Clearly, if the two wheels are driven at the same speed, the travellingobject will move in a straight line while movement through a curve canbe effected by making the voltages applied to the two motors dissimilar,The voltage difference between the two motors determines the angularvelocity difference between the two wheels and thus the radius of thecurve which will be described by the travelling object, the absolutevoltage values in turn determining the speed of the object as a whole.An undriven wheel, or a ball or a skirt arrangement serves to stabilizethe travelling object on the lower surface. In order that all the partsof the travelling object may be accommodated within a space of minimumwidth, said object preferably has a central upright at opposite sides ofwhich are mounted the driven wheels and the two electric motors, eachmotor driving a corresponding one of the two wheels through a reductiongear.

In order to minimize the packing space when a device in accordance withthe invention is used as a toy, the control panel may be given suchoverall dimensions that, when parts such as a steering wheel and a speedcontrol lever are removed, said panel has a height which is not greaterthan that of the travelling object, said panel being arranged so that itcan be swiveled towards the housing of the device for transportpurposes. With this arrangement, packing is facilitated since no specialspace is required for the control panel which would otherwise projectfrom the remainder of the device at one point. The various controlelements are removed for the purpose of transport and may be placed in abag and laid inside the box which carries the remainder of the device.

For a better understanding of the invention, and to show how the samemay be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings, in which:

FIG. I is a perspective view of a device in accordance with theinvention in the form ofa toy,

FIG. 2 is a perspective view of the lower surface of the device uponwhich the travelling object moves,

FIG. 3 is a perspective view illustrating the disposition of the uppersurface upon which the or each toy or model vehicle travels,

FIG. 4 is a side elevation of the device with a sidewall removed,

FIG. 5 is a plan view of the lower surface of the devicediagrammatically illustrating possible travelling movements of theobject,

FIG. 6 is a diagram illustrating a rotary magnet arrangement for thetransmission of signals from the travelling object to an overlying toyor model vehicle,

FIG. 7 is similar to FIG. 6 but illustrates the arrangement of a liftingmagnet for the transmission of signals from the object to an overlyingtoy or model vehicle,

FIG. 8 is a sectional elevation, to an enlarged scale, showing thetravelling object and its form of cooperation with the upper and lowersurfaces,

FIG. 9 is a sectional plan view corresponding to FIG. 8 but omitting theupper surface of the device,

FIG, 10 is a sectional elevation illustrating an alternative simplifiedform of travelling object, and

FIG. I] is an exploded perspective view illustrating the object of FIG.10 in greater detail but omitting certain of the outer parts thereof.

Referring to the drawings, the toy device which is illustrated in FIG. 1has an upper playing surface 4 which is provided with a border 5 andalso has a control panel 2 on which are mounted a steering wheel 9 and aspeed adjustment lever 8. The lever 8 and steering wheel 9 serve, ashereinafter described, to steer a toy or model vehicle in the form of atoy motor car 6 on the surface 4 around objects 7, such as trees, housesand the like, which are situated thereon. The whole toy device isconstructed as a flat box or casing I which rests upon legs 64. Ifdesired, the speed adjustment lever 8 may be replaced by a pedal and thewhole device can be constructed so that the pupil of a drivinginstructor can sit behind the wheel 9 to operate the wheel and the lever8 or equivalent pedal in accordance with the directions of the drivinginstructor.

FIG. 2 of the drawings shows a lower surface 10 upon which thetravelling object 20 (FIGS. 4, 8, 9, l0 and 11) moves. The surface 10may be a plywood panel whose upper face is coated with a ferroussheet-metal layer 13 to render it magnetically active. Alternatively, asynthetic plastics material may be used in place of plywood. Distancepieces 12 ensure the necessary spacing from an overlying upper plate 15(affording the surface 4) which is shown in FIG. 3. Wooden or plasticsidewalls ll conceal the interior of the device from users thereof.

FIG. 3 shows the upper plate I5, which affords the greater part of theupper surface 4 and which is preferably made from a transparentsynthetic plastics material. The plate 15 is clamped to the border 5 byscrews 19 or other fastenings. A second transparent plate 17, also ofmagnetically inactive material, lies above the plate 15 and road plansor the like 16 made from paper or cellulose may be sandwiched betweenthe plates 17 and 15 in such a way that they can be removed and replacedwith other such plans when required. As can be seen in FIG. 3 of thedrawings, the plate 17 is fastened to the border 5 along only one of itsedges so that it can be turned upwardly to allow ready removal of theplans 16 from therebeneath.

It can be seen from FIG. 4 of the drawings that the plate af fording thelower surface 10 rests on the legs 64 and that the travelling object 20has wheels 50. Electric current is supplied to the object 20 by way of aflexible cable 32 that is of flat striplike formation. The top of thetravelling object carries a permanent magnet 61 which cooperates with afurther permanent magnet in the floor of the toy or model motor car 6which can be seen overlying the object 20 upon the upper surface 4(plates 15 and 17).

The control panel 2 is located at the front of the device and isturnably connected to the remainder thereof by a horizontal hinge 63. Itis thus possible, for the purposes of transport, to remove the steeringwheel 9 and lever 8 from the panel 2 after which the panel can be turnedupwardly about the axis defined by the hinge 63 in the directionindicated by an arrow P in FIG. 4 of the drawings. Packing space issaved in this way, the lever 8 and steering wheel 9 being placed in abag or the like in the box which contains the remainder of the device.

FIG. 5 of the drawings shows diagrammatically various movements that thetravelling object 20 can perform upon the plate affording the lowersurface I0. FIG. 5 shows three different positions I, II and III of thetravelling object 20. In position I, the travelling object is remotefrom the control panel 2 and substantially the whole of the supply cable32 is utilized, said cable 32 extending rectilinearly. In position ll ofthe object 20, said object has just negotiated a curve and is shownpulling the cable 32 behind it, substantially the whole of the cable 32once again being unwound. In position III, however, the object 20 hasjust performed a series of rotations around its own vertical axis sothat the cable 32 has become wound around the object 20, or a partthereof, in such a way that it can readily uncoil again when required.The way in which this occurs will be evident from the followingdescription of FIGS. 8 to 11 of the drawings.

FIGS. 6 and 7 of the drawings merely illustrate diagrammatically thearrangement of magnets arranged to rotate in the direction Q (FIG. 6)and lifting magnets arranged to move in the directions indicated by thearrows in FIG. 7. These magnets serve for the transmission of signalsfrom the travelling object 20 to a toy or model vehicle equivalent tothe toy motor car 6 but having some cooperating parts that will bedriven by said magnets. The moving parts of toy or model cranes,dredgers or tipper lorries are examples of parts which can be actuatedby the magnet arrangements shown in FIGS. 6 and 7 of the drawings.

FIGS. 8 and 9 illustrate one construction of the travelling object 20from which it can be seen that said object has an upper housing half 21and a lower housing half 22. A per manent magnet 60 with the aid ofwhich the object adheres to the plate I3 (surface 10) is suspended onthe lower housing half 22, said plate 13 being made ofa ferrous materialor being covered with a layer of ferrous metal, Alternatively, the plate13 may be formed from a synthetic plastics material containing iron orferrite filings as a magnetically active filler. The upper permanentmagnet 61 acts, as previously described, through the nonmagnetic uppersurface 4 (plate 15) upon a magnet or ferrous body in the toy or modelvehicle with which the object 20 cooperates.

A ring 23 having a cylindrical outer surface surrounds the foot of thetravelling object 20 and comprises an upper ring section 24 and a lowerring section 25. Mounted on these ring sections 24 and 25, in bearings27 and 28, are a number of small rollers 26 which run in a groove formedat the junction between the upper housing half 21 and the lower housinghalf 22. The ring 23 is thus rotatable around a substantially verticalcentral axis ofthe object 20.

A contact bridge 29, 31 is mounted at one point around the ring 23 andincludes five wiping contacts 30. The contacts 30 are electricallyconnected to corresponding conductors of the cable 32 one end of whichis secured to the foot of the contact bridge 29, 31. The five contacts30 make wiping engagement with a slipring plate having five sliprings 40that are fixed around the periphery of the upper housing half 21 insuperposed relationship. Conductors 41 extend from the separatesliprings rings 40 to two motors 42, to a signal light 55 and to anyother signal transmission members (not shown) such as the members whichmove the magnets described with reference to FIGS. 6 and 7 of thedrawings.

The two motors 42 can be seen in plan in FIG. 9 of the drawings and itwill be evident that the vertical output shaft of each such motorcarries a corresponding small toothed pinion 43 whose teeth are indriving mesh with those of a much larger toothed pinion 44. Each pinion44 is mounted at the uppermost end of a corresponding shaft upon which aworm 46 is also fastened. Each worm 46 drives a corresponding worm wheel47 mounted on a horizontal driving shaft 48 of a corresponding one ofthe two driving wheels 50. The wheels 50 are located in an innercompartment 45 of the object 20 which compartment is fastened to thelower housing half 22 by struts 59. Towards the rear of the object 20,with reference to the intended direction of forward travel thereof, asmall ball 52, which is located midway between the tracks of the twowheels 50, engages the plate 13 and serves to stabilize the object 20for movement over that plate. The degree of projection of the ball 52from the bottom of the object 20 can be adjusted with the aid of a setscrew 51. The two small electric motors 42 are commutator motors whosespeeds of rotation are dependent principally upon the voltage applied tothem. Thus, when substantially equal voltage is applied to the twomotors 42, the pinions 43 will be driven at substantially the samespeeds and the object 20 will move forwardly in a straight direction.Clearly, when dissimilar voltages are applied to the two motors 42, thewheels 50 will be driven at different speeds and the object 20 willfollow a curved path whose nature will be related to the magnitude ofthe dissimilarity between the applied voltages.

FIGS. and ll of the drawings illustrate a simplified construction of thetravelling object in which an outer casing 70 is rotatable around theremainder of the object with the aid of a vertical sleeve bearing 71located centrally at the top of the object. The bearing 71 also carriesthe upper magnet 61. A post 72 projects downwardly from the top of theouter rotatable casing 70 into the interior of that casing and has threeconductors fastened to it, said conductors forming part of a flatstriplike cable 73 which is entered through a hole in the side of thecasing 70 and effectively anchored to said post 72. The bare ends of thethree conductors which are supported by the post 72 afford contactswhich make wiping engagement with three superposed sliprings 74 whosearrangement can be seen best in the exploded view of FIG. 11. The threesliprings 74 are maintained apart by spacers 75 and all of them surrounda central upright 76 of the object 20 which is located beneath thebearing 71 when the object is assembled. It will be evident from FIG. 10of the drawings that the outer casing 70 has a cylindrical outer surfacearound which the cable 73 can wind, when required, to prevententanglement of that cable. The cable 73 may conveniently, but notessentially, be formed from a length of the material which iscommercially available in Great Britain under the Trade NameBICCASTRIP." The cable 73 may have a length of about 18 inches (46centimeters).

The object 20 has an upper portion 77 and a lower portion 81 which areboth preferably formed from synthetic plastics materials, the two motors42 being lodged between said portions 77 and 8] at opposite sides of thecentral upright 76. In this case, the output shafts of the two motors 42are horizontally disposed and they transmit their drive to wheels 78(which are provided with tires that are not shown) through theintermediary of simple reduction gearing that is generally indicated bythe reference 79.

Instead of providing the stabilizing ball 52, or an equivalent smallwheel, the object 20 is stabilized on the plate I3 by a skirt 80 (FIG.10) which projects downwardly from the lower portion 81 alongside theinterior of the outer casing 70. The foot of said skirt 80 slides overthe plate 13 and provides an adequate degree of stability in associationwith the magnet 60 that effects magnetic adhesion of the object 20 tosaid magnetically active plate 13.

It will be evident that, in the case of the simplified travelling object20 which is shown in FIGS. 10 and 11 of the drawings, two of the threeconductors forming part of the cable 73 transmit voltage from thecontrol panel 2 to the corresponding motors 42 while the third conductoris a common earth, ground or negative conductor. Although this simpleconstruction is adequate to control both the steering and speed of a toyor model vehicle, it will be appreciated that further conductors couldbe provided for cooperation with further sliprings 74 to operateadditional parts, such as the signal light 55 illustrated in FIG. 8, ifso desired.

Iclaim:

1. In a device having a first extending surface, a second extendingsurface, a manually operable control panel, motordriven means for movingon said first surface in response to electrical signals received fromsaid panel, toy vehicle means for moving on said second surface, meansassociated with said toy vehicle means and said motor driven means forcausing said toy vehicle means to move on said second surface with saidmotor-driven means as said motor-driven means moves on said firstsurface, a multiple slip ring mounted on said motor driven moving meansand having a plurality of contacts each extending around the peripheryof said motor driven means, a flexible cable member having a striplikeformation, having a plurality of individual electrical connectors,extending substantially perpendicular to said first surface, andconnected to said panel means for carrying said electrical signals, theimprovement comprising:

cable member means having a cylindrical outer surface for receiving thewound cable member mounted about the periphery of said motor-drivenmeans for free rotation about said periphery, so that movement of saidmotor driven means when at least a portion of said cable member is woundabout said outer surface and said cable member does have slack not woundon said outer surface causes said cable member means to rotate andunwind said cable member and having a plurality of electrical contactseach connecting one of said individual conductors to one of saidcontacts of said slipring.

2. In a device as claimed in claim I], wherein said causing meansincludes an upwardly directed permanent magnet and a magnetically activeportion of said toy vehicle means and wherein said second surfaceoverlies said motor driven means and is formed from a magneticallyinactive material.

3. In a device as claimed in claim 11, wherein said first surface ismagnetically active, and said motor driven means includes a magneticelement designed to cooperate with said first surface and cause magneticadhesion of the motor driven means thereto.

4. In a device as claimed in claim 11, wherein said second surface isformed from a magnetically inactive material.

5. In a device as claimed in claim 11, wherein said multiple slipringsurrounds said motor driven means in substantially concentricrelationship therewith, and wherein said member means includes a ringthat is rotatable relative to said motordriven means and that carries acontact bridge affording support for said motor-driven means, wherebythe contacts of said bridge will make wiping engagement with thesliprings during rotation of said ring around said motor driven means.

6. In a device as claimed in claim 5, wherein the multiple 8. In adevice as claimed in claim 7, wherein said motorsllpl'lng is arranged ona central "P of Said motor-driven driven means includes an undriven ballfor stabilizing said ohmeans which also includes a post fastened to anouter casing j t i iation igh the two wheels.

which is rotatable around the remainder of said motor-driven means, saidpost supporting the contacts of said bridge in such a way that they makewiping engagement with said contacts of said slipring during rotation ofsaid casing around the remainder of said motor-driven means.

7. in a device as claimed in claim ll, wherein the motordriven means hastwo juxtaposed and individually driven wheels.

9. In a device as claimed in claim 7, wherein said motordriven meansincludes a skirt which serves for stabilizing said object in associationwith the two wheels.

10. In a device as claimed in claim 7, wherein the two wheels are drivenby corresponding electric motors through 0 the intermediary of reductiongearing.

1. In a device having a first extending surface, a second extendingsurface, a manually operable control panel, motordriven means for movingon said first surface in response to electrical signals received fromsaid panel, toy vehicle means for moving on said second surface, Meansassociated with said toy vehicle means and said motor driven means forcausing said toy vehicle means to move on said second surface with saidmotordriven means as said motor-driven means moves on said firstsurface, a multiple slip ring mounted on said motor driven moving meansand having a plurality of contacts each extending around the peripheryof said motor driven means, a flexible cable member having a striplikeformation, having a plurality of individual electrical connectors,extending substantially perpendicular to said first surface, andconnected to said panel means for carrying said electrical signals, theimprovement comprising: cable member means having a cylindrical outersurface for receiving the wound cable member mounted about the peripheryof said motor-driven means for free rotation about said periphery, sothat movement of said motor driven means when at least a portion of saidcable member is wound about said outer surface and said cable memberdoes have slack not wound on said outer surface causes said cable membermeans to rotate and unwind said cable member and having a plurality ofelectrical contacts each connecting one of said individual conductors toone of said contacts of said slipring.
 2. In a device as claimed inclaim 11, wherein said causing means includes an upwardly directedpermanent magnet and a magnetically active portion of said toy vehiclemeans and wherein said second surface overlies said motor driven meansand is formed from a magnetically inactive material.
 3. In a device asclaimed in claim 11, wherein said first surface is magnetically active,and said motor driven means includes a magnetic element designed tocooperate with said first surface and cause magnetic adhesion of themotor driven means thereto.
 4. In a device as claimed in claim 11,wherein said second surface is formed from a magnetically inactivematerial.
 5. In a device as claimed in claim 11, wherein said multipleslipring surrounds said motor driven means in substantially concentricrelationship therewith, and wherein said member means includes a ringthat is rotatable relative to said motor-driven means and that carries acontact bridge affording support for said motor-driven means, wherebythe contacts of said bridge will make wiping engagement with thesliprings during rotation of said ring around said motor driven means.6. In a device as claimed in claim 5, wherein the multiple slipring isarranged on a central upright of said motor-driven means which alsoincludes a post fastened to an outer casing which is rotatable aroundthe remainder of said motor-driven means, said post supporting thecontacts of said bridge in such a way that they make wiping engagementwith said contacts of said slipring during rotation of said casingaround the remainder of said motor-driven means.
 7. In a device asclaimed in claim 11, wherein the motor-driven means has two juxtaposedand individually driven wheels.
 8. In a device as claimed in claim 7,wherein said motor-driven means includes an undriven ball forstabilizing said object in association with the two wheels.
 9. In adevice as claimed in claim 7, wherein said motor-driven means includes askirt which serves for stabilizing said object in association with thetwo wheels.
 10. In a device as claimed in claim 7, wherein the twowheels are driven by corresponding electric motors through theintermediary of reduction gearing.